Conductive barrier direct hybrid bonding

ABSTRACT

A method for forming a direct hybrid bond and a device resulting from a direct hybrid bond including a first substrate having a first set of metallic bonding pads, preferably connected to a device or circuit, capped by a conductive barrier, and having a first non-metallic region adjacent to the metallic bonding pads on the first substrate, a second substrate having a second set of metallic bonding pads capped by a second conductive barrier, aligned with the first set of metallic bonding pads, preferably connected to a device or circuit, and having a second non-metallic region adjacent to the metallic bonding pads on the second substrate, and a contact-bonded interface between the first and second set of metallic bonding pads capped by conductive barriers formed by contact bonding of the first non-metallic region to the second non-metallic region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/835,379, filed on Aug. 25, 2015, the entire contents of which areincorporated by reference. This application is related to applicationsSer. Nos. 09/505,283, 10/359,608 and 11/201,321, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the field of direct bonding, morespecifically hybrid direct bonding, preferably at room or lowtemperature, and more particularly to the bonding of semiconductormaterials, devices, or circuits to be utilized in stacked semiconductordevice and integrated circuit fabrication and even more particularly tothe fabrication of value-added parts in consumer and business productsincluding image sensors in mobile phones, RF front ends in cell phones,3D memory in high performance graphics products, and 3D memory inservers.

Description of the Related Art

Die, chip, or wafer stacking has become an industry standard practice tothe continuing demands of increased functionality in a smaller formfactor at lower cost. In general, stacking can be done with electricalinterconnections between layers in the stack formed either as part ofthe stacking process or after the stacking process. An example ofelectrical interconnections formed after the stacking process is the useof through silicon via (TSV) etching and filling through one layer inthe stack and into an adjacent layer in the stack to make electricalinterconnections between layers in the stack. Examples of these threedimensional (3D) electrical interconnections formed as part of thestacking process include solder bumps and copper pillar, either with orwithout underfill, hybrid bonding and direct hybrid bonding. Realizationof the 3D electrical interconnections as part of the stacking process isadvantageous for a number of reasons including but not limited toeliminating the cost and exclusion requirements of TSV (through siliconvia) technology. Direct hybrid bonding, also referred to as Direct BondInterconnect (DBI®), is advantageous over other forms of stacking for anumber of reasons including but not limited to a planar bond over metaland dielectric surface components that provides high strength at lowtemperature and enables 3D interconnect pitch scaling to submicrondimensions.

The metal and dielectric surface components used for a direct hybridbond can be comprised of a variety of combinations of metals anddielectrics in a variety of patterns formed with a variety offabrication techniques. Non-limiting examples of metals include copper,nickel, tungsten, and aluminum. See for example; P. Enquist, “HighDensity Direct Bond Interconnect (DBI™) Technology for Three DimensionalIntegrated Circuit Applications”, Mater. Res. Soc. Symp. Proc. Vol. 970,2007, p. 13-24; P. Gueguen, et. al., “3D Vertical Interconnects byCopper Direct Bonding,” Mater. Res. Soc. Symp. Proc. Vol. 1112, 2009, p.81; P. Enquist, “Scalability and Low Cost of Ownership Advantages ofDirect Bond Interconnect (DBI®) as Drivers for Volume Commercializationof 3-D Integration Architectures and Applications”, Mater, Res. Soc.Symp. Proc. Vol. 1112, 2009, p. 81; Di Cioccio, et. al., “Vertical metalinterconnect thanks to tungsten direct bonding”, 2010 Proceedings60^(th) ECTC, 1359-1363; H. Lin, et. al., “Direct Al—Al contact usinglot temperature wafer bonding for integrating MEMS and CMOS devices,”Microelectronics Engineering, 85, (2008), 1059-1061. Non-limitingexamples of dielectrics include silicon oxide, silicon nitride, siliconoxynitride, and silicon carbon nitride. See for example P. Enquist, “3DTechnology Platform—Advanced Direct Bond Technology”, C. S. Tan, K.-N.Chen, and S. J. Koester (Editors), “3D Integration for VLSI Systems,”Pan Stanford, ISBN 978-981-4303-81-1, 2011 and J. A. Ruan, S. K. Ajmera,C. Jin, A. J. Reddy, T. S. Kim, “Semiconductor device having improvedadhesion and reduced blistering between etch stop layer and dielectriclayer”, U.S. Pat. No. 7,732,324, B2 Non-limiting examples of a varietyof patterns include arrays of vias or arrays of metal lines and spaces,for example as found in via and routing layers in CMOS back-end-of-line(BEOL) interconnect fabrication. Within these examples, 3D electricalinterconnections may be formed by alignment and bonding of metal vias tometal vias, metal vias to metal lines, or metal lines to metal lines.Non-limiting examples of fabrication techniques to build a surfacesuitable for a hybrid bond are industry standard single and dualdamascene processes adjusted to satisfy a suitable topographyspecification, if necessary.

There are basically two types of CMOS BEOL fabrication processes. One istypically referred to as an aluminum (Al) BEOL and the other is referredto as a copper (Cu) BEOL. In an Al BEOL process, Al with a suitableconductive barrier layer is typically used as the routing layer andtungsten (W), with a suitable conductive barrier layer is used for a vialayer to electrically interconnect between two adjacent Al routinglayers. The Al routing layer is typically dry etched and subsequentlyplanarized with a dielectric deposition followed by chemo-mechanicalpolishing (CMP). The W via layer is typically formed with a singledamascene process comprised of dielectric deposition, via patterning andetching to the previous routing layer, via filling with conductivebarrier layer physical vapor deposition and W chemical vapor deposition,and CMP of W and conductive barrier layer to isolate W vias, or plugs,within the dielectric matrix. In a Cu BEOL process, Cu with a suitableconductive barrier layer is typically used as the routing and via layer.The Cu routing and via layers are typically formed with a dual damasceneprocess comprised of dielectric deposition, via patterning and etchingpartially through the dielectric layer, followed by routing patterningthat overlaps the via patterning and simultaneous continued etching ofthe via(s) to the previous routing layer where the routing overlaps thepartially etched vias and etching of a trench for routing that connectsto the previous routing layer with the via. An alternate dual damasceneprocess is comprised of dielectric deposition, routing patterning andetching partially through the dielectric layer that stops short of theprevious routing layer, via patterning and etching to the previousrouting layer where the via is within the partially etched routing andthe etching completes the via etch to the previous routing layer. Eitherdoubly etched surface is then filled with a conductive barrier layer,for example by physical vapor deposition, followed by Cu filling, forexample by electroplating or physical vapor deposition andelectroplating, and finally CMP of the Cu and conductive barrier layerto isolate Cu routing within the dielectric matrix.

Use of either the industry standard W and Cu damascene process flowsdescribed above can be used to form a surface for hybrid bonding,subject to a suitable surface topography, for example as provided above.However, when these surfaces are used for hybrid bonding, there willtypically be a heterogeneous bond component between metal on one surfaceand dielectric on the other surface, for example due to misalignment ofvia surfaces. This can result in via fill material from one bond surfacein direct contact with dielectric from the other bond surface andwithout an intervening conductive barrier that is elsewhere between theCu or W filled via and the surrounding dielectric.

It is preferable to have a wide process window with a low thermal budgetfor a direct hybrid bond process technology leveraging materials andprocesses that are currently qualified in a CMOS BEOL foundry to lowerthe adoption barrier for qualifying a direct hybrid bond process in thatfoundry. A Cu BEOL process is an example of such a preferable capabilitydue to the Cu damascene process which has been an industry standard fora number of years and the capability of Cu direct hybrid bond technologyto leverage this infrastructure. It has been relatively more challengingto leverage an Al BEOL industry standard process because the two primarymetals in this process, W and Al, are more challenging materials todevelop either a W or Al direct hybrid bond technology due to acombination of factors including high yield strength, coefficient ofthermal expansion (CTE), native oxide, and hillock formation.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed to a method of forming adirect hybrid bond surface including forming a first plurality ofmetallic contact structures in an upper surface of a first substrate,where a top surface of said structures is below said upper surface;forming a first layer of conductive barrier material over said uppersurface and said plurality of metallic contact structures; and removingsaid first layer of conductive barrier material from said upper surface.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic depiction of a cross-section of the near surfaceregion of a single or dual damascene process formed conductive layers,with filled vias and/or routing with a conductive barrier between filledvias and/or routing and surrounding dielectric;

FIG. 2 is a schematic depiction of the cross-section in FIG. 1 afterremoval of the conductive layers from the surface of a surroundingdielectric;

FIG. 3 is a schematic depiction of the cross-section in FIG. 2 afterforming a conductive barrier material layer;

FIG. 4 is a schematic depiction of the cross-section in FIG. 3 afterremoval of the conductive barrier layer material layer from the surfaceof the surrounding dielectric;

FIG. 5 is a schematic depiction of two hybrid direct bond surfaces beingbonded;

FIG. 6 is a schematic depiction of two hybrid direct bond surfaces aftercontacting the respective dielectric layers;

FIG. 7 is a schematic depiction of two hybrid direct bond surfacesdirectly bonded;

FIG. 8 is a schematic depiction of curvature of the upper surface of theconductive barrier material as a result of dishing;

FIG. 9 is a schematic depiction of a pair of substrates, according tothe present invention, with misalignment of similar via structures withconductive barriers and alignment of vias with conductive barriers torouting structures with conductive barriers;

FIG. 10 is a schematic depiction of a cross-section of the near surfaceregion of a surface comprised of a patterned metal layer planarized withsurrounding dielectric with planarization exposing patterned metallayer, without a conductive barrier layer laterally between metal layerand surrounding dielectric;

FIG. 11 is a schematic depiction of the cross-section in FIG. 10 withthe conductive portion of the exposed surface of the patterned metallayer capped with conductive barrier metal according to the presentinvention;

FIG. 12 is a schematic depiction of a pair of contacted substrates,according to the present invention, with an example of alignment ofrouting structures without conductive barriers to routing structureswithout conductive barriers laterally between metal layer andsurrounding dielectric;

FIG. 13 is a schematic depiction of another embodiment of the inventionhaving a through silicon via structure;

FIG. 14 is a schematic depiction of the structure of FIG. 13 with asecond conductive barrier material layer; and

FIG. 15 is a schematic depiction of another embodiment of the inventionhaving a through silicon via structure with a dielectric layer on thesidewall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designatelike or corresponding parts throughout the several views, and moreparticularly to FIG. 1 showing a cross-section of a surface of asubstrate 30 in a process for direct hybrid bonding according to theinvention comprised of conductor 1, conductive barrier 2, dielectric 3,and metal structure 4. Metal structures 4 are formed in dielectric 3.Metal structures 4 are located within dielectric 3 and can be a contact,pad, line, or other metal interconnect structure. Openings are formed indielectric 3 over metal structures 4 followed by formation of barrier 2and conductor 1. The sizes and thicknesses of the conductor 1,conductive barrier 2 and metal structure 4 are not to scale but aredrawn to illustrate the invention. While the openings and metalstructures are shown to be the same size and shape, they can differ insize and shape depending upon design or need.

A wide variety of metals for conductor 1 are possible including but notlimited to Cu, and W which are common in Cu and Al BEOL foundries,respectively. Cu can be deposited by physical vapor deposition (PVD) orelectroplating (EP) and W can be deposited by chemical vapor deposition(CVD). A wide variety of conductive barriers for conductive barriermaterial 2 are also possible which are common in Cu and Al BEOLfoundries. Conductive barriers in Cu BEOL processes include tantalum(Ta), titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride(WN), ruthenium oxide (RuO₂), tantalum silicon nitride (TaSiN), titaniumsilicon nitride (TiSiN), tungsten boron nitride (TBN), cobalt tungstenboride (CoWB), cobalt tungsten phosphide or combinations thereof, forexample Ti/TiN and Ta/TaN, which can be deposited by a variety oftechniques including PVD, CVD, and metal organic CVD (MOCVD). A varietyof PVD techniques are available including DC magnetron sputtering,collimated sputtering, and ionized metal plasma (IMP). Conductivebarriers in Al BEOL processes include Ti/TiN. Other materials are alsopossible as barriers, for example nickel (Ni).

A wide variety of dielectrics are also possible including but notlimited to silicon oxide, silicon nitride, and silicon carbide nitridewhich are common in Cu and Al BEOL foundries. A common method to createthe surface described by the cross-section in FIG. 1 is with thedamascene process described above.

The upper surface of FIG. 1 is subjected to CMP to remove the portion ofconductor 1 and conductive barrier 2 on top of dielectric 3. FIG. 2illustrates the structure after CMP. The relative heights of conductor 1and conductive barrier 2 relative to dielectric 3 can be controlled bythe CMP portion of the damascene process.

There are a number of configurations of relative height of the conductor1 and conductive barrier 2 to dielectric 3. The top surfaces ofconductor 1 and barrier 2 can be below, even with, nominally even withor above the surface of dielectric 3. In general, direct hybrid bondingis possible with all configurations. However, a preferred configurationis where the relative heights of conductor 1 and conductive barrier 2are below dielectric 3 by a distance t1. This configuration is conduciveto formation of a void-free bond interface and is more manufacturablewith regard to variation of the relative height across the bond surface.An example of variation of relative height across the bond surface ofthe conductive layers below dielectric 3 for a surface most suitable fordirect hybrid bonding is one to ten nanometers below the dielectric 3,although smaller and larger variations are also possible. This recess istypically referred to as dishing. The resulting surface is referred toas a hybrid bond surface without a conductive barrier 2.

A typical amount of dishing compatible with hybrid bonding is 0 to 20nm, referred to as standard dishing. Standard dishing is increased by anamount that is comparable to the thickness of a subsequent conductivebarrier 7 shown in FIG. 3 formed on top of this increased dishingforming openings 5 shown in FIG. 2 resulting in a dishing that iscomparable to the standard dishing and compatible with that desired fora direct hybrid bond. An example of an increase in standard dishing is5-20 nm, resulting in a total dishing t1 of about 5-40 nm. This increasein standard dishing can be formed in a variety of ways, for example byincreasing the CMP used to create the standard dishing until the desiredincreased dishing is achieved. This increase in CMP can be accomplishedwith an increase in CMP time, the amount of which can be determined byroutine calibration and can be a function of CMP pad, slurry, downforce,carrier and table rotation, and pattern of conductor and dielectric onthe hybrid surface.

As shown in FIG. 3, a layer of conductive barrier metal 6 is formed overthe structure on surface 31 shown in FIG. 2. Barrier 6 can be the sameor a different material than conductive barrier 2. Formation of barrier6 on top of the conductor 1 after increased dishing can be formed in anumber of ways, for example by a damascene process including depositionof the conductive barrier over the entire surface followed by CMP toremove the conductive barrier from the higher dielectric surface withoutremoving a significant amount or all of the conductive barrier materialof layer 6 from within the recess. The barrier formation may also beformed with a selective process, for example electro-less nickelelectroplating. The resulting structure has conductive barrier 7 in eachof the openings 5 on top of conductor 1 and conductive barrier 2. Thisresulting dishing is preferably compatible with that required for adirect hybrid bond, i,e, the surface of conductive barrier 7 is lessthan 20 nm, and preferably 1-10 nm, below the surface of dielectric 3.The cross-section of the resulting surface shown schematically in FIG. 4is referred to as a hybrid bond surface with a conductive barrier 7.

The thickness of the layer 6 can be less than the amount of dishing ofconductor 1/barrier 2, as shown in FIG. 3, or can be the same as orthicker than this amount of dishing. In the former case, only a portionor none of the layer 6 is removed from the recess. In the case of thelayer 6 being the same or thicker than the amount of recess, layer 6 isremoved from within the recess by the CMP. Layer 6 is removed in allcases so that the resulting dishing is less than 20 nm, preferably 1-10nm, in forming barrier 7.

Each hybrid bond surface of substrate 30 can contain devices and/orintegrated circuits (not shown) such that these devices and/orintegrated circuits can be connected to each other after completion ofthe hybrid bond. The devices and circuits can contain metal structures 4or can be connected to metal structures 4 through further unillustratedinterconnect structures.

Two hybrid bond surfaces of substrates 30 and 32 each having with aconductive barrier 7 with cross-section schematic such as shown in FIG.4 can now be direct hybrid bonded to each other as shown in thecross-sections of FIGS. 5 and 6 to form direct hybrid bond 12.Substrates 30 and 32 are aligned (FIG. 5) and placed into direct contactsuch that the dielectric layers 3 in substrates 30 and 32 contact eachother (FIG. 6). The alignment and contacting can be performed at roomtemperature in either room ambient or under vacuum. Although the figuresschematically show a gap between the barriers 7 of substrates 30 and 32,there may be partial or significant contact between barriers 7 followingthe alignment and contacting. While a one-to-one connection arrangementis shown in FIG. 6, other arrangements are possible such as plural metalstructures in one substrate are bonded to a single metal structure inanother substrate.

The dielectric surfaces of substrates 30 and 32 are preferably preparedas described in application Ser. Nos. 09/505,283, 10/359,608 and11/201,321. Briefly, the surfaces may be etched, polished, activatedand/or terminated with a desired bonding species to promote and enhancechemical bonding between dielectric 3 on substrates 30 and 32. Smoothsurfaces of dielectric 3 with a roughness of 0.1 to 3 nm rms areproduced which are activated and/or terminated through wet or dryprocesses.

As the substrate surfaces contact at room temperature, the dielectric 3of the substrate surfaces began to form a bond at a contact point orpoints, and the attractive bonding force between the wafers increases asthe chemically bonded area increases. This contact can include barriers7 or not include barriers 7. If the contact includes barriers 7, thepressure generated by the chemical substrate-to-substrate bonding indielectric 3 results in a force by which contacting areas of thebarriers 7 are strongly joined, and the chemical bonding between thedielectric 3 in substrates 30 and 32 produces electrical connectionbetween metal pads on the two different wafers.

The internal pressure of barriers 7 against each other resulting fromthe bond between the dielectric 3 of substrates 30 and 32 may not beadequate to achieve an electrical connection with a preferably lowresistance due to, for example, a native oxide or other contamination,for example, hydrocarbons. An improved bond or preferably lowerresistance electrical connection may be achieved by removing the nativeoxide on barrier 7. For example, dilute hydrofluoric acid may be used toclean the surface or the surfaces of substrates 30 and 32 may be exposedto an inert ambient, for example nitrogen or argon, after removing thenative oxide until bonding is conducted.

The internal pressure also may not be sufficient to contact enough ofthe surfaces of barriers 7 to each other. Alternatively or in addition,an improved bond or preferably lower resistance electrical connectionbetween barriers 7 can be achieved by heating. Examples of heatinginclude temperatures in the range of 100-400° C. for times between 10minutes and 2 hours depending upon the materials used for the contactstructures 4, barrier 6 and conductor 1. Time and temperatureoptimization for a given combination of materials is possible. Forexample, shorter heating times may be possible with higher temperaturesand lower temperatures may be possible with longer heating times. Theextent to which heating time can be minimized and/or heating temperaturecan be minimized will depend on the specific structure and materialscombination and can be determined with common process optimizationpractices. For example, if barrier 7 is nickel, a temperature of 300° C.for two hours may be sufficient or a temperature of 350° C. for 15minutes may be sufficient to improve the bond and improve the electricalconnection. Higher and lower temperatures and/or times are also possibledepending on barrier 7 material and other materials underneath barrier7. Temperature increase can result in a preferably low resistanceelectrical connection by reduction of the native oxide or othercontamination or by increasing the internal pressure between barriers 7due to thermal expansion of conductor 1 and barrier 7. Material 4 andother materials below material 4 (not illustrated) may also increase thethermal expansion of the structure underneath barrier 7 andcorrespondingly increase pressure between opposed barriers 7. Forexample, if material 4 is aluminum with associated CTE and Young'smodulus, a higher pressure may be generated compared to an alternatematerial 4 with a lower CTE and/or Young's modulus. Heating may alsoincrease interdiffusion between barriers 7 to produce in a preferablelower-resistance electrical connection.

If the initial bond between the dielectric 3 of substrates 30 and 32does not include barriers 7, heating can be used to result in contactbetween barriers 7 due to a higher CTE of barrier 7 than dielectric 3.The amount of heating or temperature rise depends on the separationbetween barriers 7, the thickness, CTE, and Young's modulus of barriers7 and conductor 1 and metal structure 4 as these parameters affect thepressure between opposed barriers 7 for a given temperature rise. Forexample, minimizing the separation between barriers 7, for example lessthan 10 nm, may reduce the heating compared to a separation of 20 nm. Asa further example, the height or thickness of barrier 7 and/or conductor1 will increase pressure as the thermal expansion of barrier 7 andconductor 1 will increase with thickness. For example, the typicalincrease of expansion of barrier 7 and conductor 1 is proportional tothickness. As a further example, conductor 1 with higher Young's modulusis expected to generate higher pressure than an alternate conductor 1with lower Young's modulus as the higher Young's modulus material isless likely to yield when generating pressure. A barrier 7 with lowerYoung's modulus may not require as much heating as it may facilitateforming a connection by yielding at a lower pressure. Following heating,the thermal expansion of conductor 1 and barrier 7 thus result inintimately contacted low-resistance connections, as shown in FIG. 7 ifbarriers 7 are not in intimate contact when the surfaces of substrates30 and 32 are initially contacted.

While the surfaces of conductors 1/barrier 2 and barriers 7 are shown asplanar in the above examples, one or both may have some curvature due tothe CMP process. A profile is shown in FIG. 8 where both have curvature.In FIG. 8, substrate 33 is shown having barrier 7 and conductor1/barrier 2 whose surfaces vary. The thickness of barrier 7 ispreferably thick enough to accommodate coverage of the roughness ofconductor 1 but not too thick to complicate fabrication. Typicalthickness ranges can be 5-20 nm. The relative thickness of the barrierat the middle and edge of the curvature can be thicker or thinnerdepending on the curvature of formation of surface of contact 1 prior tobarrier 7 deposition on conductor 1 and curvature of formation ofbarrier 7, for example due to different characteristics of a CMP processused to form surface of contact 1 and CMP process used to form surfaceof barrier 7. The center of the barrier 7 is recess less than 20 nm andpreferably 1-10 nm below the surface of dielectric 3.

FIG. 9 illustrates the upper portion of two substrates 34 and 35 withhybrid bond surfaces. Hybrid bond surfaces with a conductive barrier cancomprise via components 8 that are connected to underlying tracecomponents (not shown) or trace components 9 that are connected tounderlying via components (not shown). After bonding, there is typicallysome amount of misalignment between respective hybrid bond surfaces witha conductive barrier. This misalignment can result in contact ofconductive barrier 7 on a first hybrid bond surface with a dielectricsurface 6 on a second hybrid bond surface and contact of a dielectricsurface 6 on a first hybrid bond surface with a conductive barrier 7 ona second hybrid bond surface as shown by 10 in FIG. 9. This misalignmentcan also result in contact of conductive barrier 7 on one hybrid bondsurface with dielectric surface 6 on another surface and the contact ofan entire surface of conductive barrier 7 from one surface with aportion of a surface of a conductive barrier 7 on the other hybrid bondsurface as shown by 11 in FIG. 9.

Notwithstanding this misalignment, the surface of dielectric 3 on eitherfirst or second hybrid bond surface is in contact with either conductivebarrier 7 on the other hybrid bond surface and conductive barrier 7 oneither first or second hybrid bond surface is in contact with eitherconductive barrier 7 or the surface of dielectric 3 on the other hybridbond surface according to the present invention. The conductive barrier7 on top of conductor 1 thus prevents contact between conductor 2 anddielectric 3 notwithstanding misalignment. This feature of the subjectinvention can improve reliability of the direct hybrid bond, for examplewhen Cu is used as conductor 1 with Cu single or dual damascene directhybrid bond surfaces built in a Cu BEOL for applications where there isa concern, for example, of Cu diffusion into dielectric 3 if Cu was indirect contact with dielectric 3. The feature may also facilitate theformation of an electrical connection across the bond interface for somestructures, for example where conductor 1 is a W plug single damascenedirect hybrid bond surfaces built in an Al BEOL when making electricalconnections between conductor 1 on opposing surfaces is more challengingthan making electrical connections between conductive barriers 7 on topof conductors 1 on opposing surfaces.

The amount of dishing shown in FIG. 2 can affect the thermal budget of asubsequent direct hybrid bond using these surfaces with recessedconductive portions. For example, after initially placing direct hybridbond surfaces into direct contact, the dielectric portions may be indirect contact and all or some of the recessed conductive portions maynot be in direct contact due to the recess. Heating of these directhybrid bonded surfaces with recessed conductive portions can result inexpansion of the recessed conductive portions so that they are broughtinto direct contact at a temperature above that at which the directhybrid bond surfaces were brought into contact and generate significantpressure to facilitate electrical connection between opposed recessedconductive portions and even higher temperatures. These highertemperatures can facilitate the formation of electrical interconnectionsbetween opposed recessed conductive portions and completion of thedirect hybrid bond. The temperatures required to bring the recessedportions into direct contact and to generate significant pressure tofacilitate electrical connection between opposed recessed conductiveportions is a combination of the conductive material, residual or nativeoxide on the conductive material, yield strength of the conductivematerial and dishing or recess of the conductive material. For example,less dishing can result in a lower thermal budget required to completethe hybrid bond after initially directly bonding opposed dielectricsurfaces at low or room temperature due to less conductor 1 andconductive barrier 7 expansion required to form a metallic bond betweenopposed conductive barrier 7 surfaces.

For example, when using Ni as a conductive barrier, 10 nm of recess maybe accommodated by heating to about 350° C. compared to about 200° C.which can be sufficient if using copper without a capping conductivebarrier. In order to reduce the thermal budget it is generally useful touse a higher CTE (coefficient of thermal expansion) material with loweryield strength and less dishing. In general, the CTE and yield strengthare given by the barrier chosen and the dishing is a variable that canbe varied to achieve a suitable thermal budget. The thermal budget canalso be influenced by materials that are underneath the conductor. Forexample, conductors 1 with higher CTE (i.e., above 15 ppm/° C.)underneath conductor 1, for example metal structure 4 as shown in FIG.4, may have a lower thermal budget to form hybrid bond electricalconnections than conductors 1 and/or metal structures 4 with a lowerCTE. Examples of metals with high CTE above 15 ppm/° C. include Cu andAl which are conductors common in Al and Cu BEOL processes.

In a second embodiment according to the invention, a conductive portion13 surrounded by a dielectric portion 14 comprises a direct hybrid bondsurface 15 in substrate 36 as shown in FIG. 10. An example of conductiveportion 13 is aluminum and an example of dielectric portion 14 is aninter-layer dielectric, examples of which are silicon oxide and otherdielectrics used in Al BEOL, which are examples of typical materialsused in Al BEOL. The metal portion 13 may include via and/or routingpatterns connected to underlying layers of interconnect. The dielectricportion 14 may be contiguous, for example if the conductive portion iscomprised only of vias, or may not be contiguous, for example if theconductive portion is separated by routing patterns. In this embodimentdirect hybrid bond surface 15 preferably has a dished conductive portionwithin a direct hybrid bonding specification. This surface can be formedby a combination of an Al metallization, dielectric deposition, and CMPplanarization to form the surface with cross-section shown in FIG. 10.The Al metallization may include a conductive barrier on top, forexample Ti. If there is a conductive barrier and it is removed by theCMP planarization, the surface will have a cross-section shown in FIG.10. If the conductive barrier is sufficiently thick that it is notentirely removed by the CMP planarization, and there is suitable dishingt2, for example 0-20 nm of the conductive barrier portion of the hybridbond surface for hybrid bonding, then this surface, e.g, as shown inFIG. 11, can be suitable for direct hybrid bonding without additionalconductive barrier deposition and CMP.

The dishing t2 described in FIG. 10 is increased by an amount that iscomparable to the thickness of a subsequent conductive barrier 16 thatis formed on top of this increased dishing resulting in a dishing thatis comparable to that in FIG. 10 and compatible with that required for adirect hybrid bond (FIG. 10). This increase in thickness is in the rangeof about 5-20 nm. This increase in standard dishing can be formed in avariety of ways, for example by increasing the amount of CMP from thatused to be compatible with that required for a direct hybrid bond.Formation of the barrier on top of the increased dishing can be formedin a number of ways, for example by a damascene process includingdeposition of the conductive barrier over the entire surface (similar toFIG. 3) followed by CMP to remove the conductive barrier from the higherdielectric surface 17 without removing a significant amount or all ofthe conductive barrier from within the recess (FIG. 11). The thicknessof the formed barrier can be comparable to, greater than, or less thanthe increased dishing thickness, for example less than about 40 nm. Thefinal barrier thickness and the dishing can then be controlled by CMPafter formation of the barrier.

In this embodiment, this resulting dishing is preferably compatible withthat required for a direct hybrid bond. A cross-section of the resultingsurface is shown schematically in FIG. 11 illustrating substrate 37 andis referred to as a hybrid bond surface 18 with a conductive barrier 16not in contact with an underlying conductive barrier. The barrierformation may also be formed with a selective process, for exampleelectro-less nickel electroplating.

Two hybrid bond surfaces of substrates 38 and 39 with a conductivebarrier 16 formed as shown in the cross-section schematic of FIG. 11 cannow be direct hybrid bonded to each other as shown in the cross-sectionof FIG. 12 to form direct hybrid bond with conductive barrier 16 withoutan underlying conductive barrier. Each hybrid bond surface is a surfaceof a substrate and each substrate can contain devices and/or integratedcircuits such that these devices and/or integrated circuits can beconnected to each other after completion of the hybrid bond. Hybrid bondsurfaces with a conductive barrier can comprise via components that areconnected to underlying trace components (not shown) or trace components19 that are connected to underlying via components (not shown).

After bonding, there is typically some amount of misalignment betweenrespective hybrid bond surfaces with a conductive barrier. Thismisalignment can result in contact of conductive barrier 16 on a firsthybrid bond surface with a dielectric surface 17 on a second hybrid bondsurface in substrate 36 and contact of a dielectric surface 17 on afirst hybrid bond surface with a conductive barrier 16 on a secondhybrid bond surface as shown by 20 in FIG. 12. This misalignment canalso result in contact of conductive barrier 16 on one hybrid bondsurface with dielectric surface 17 on another surface and the contact ofan surface of conductive barrier 16 from one surface with a portion of asurface of a conductive barrier 16 on the other hybrid bond surface asshown by 21 in FIG. 12.

Notwithstanding this misalignment, dielectric surface 17 on either firstor second hybrid bond surface is in contact with either conductivebarrier 16 on the other hybrid bond surface and conductive barrier 16 oneither first or second hybrid bond surface is in contact with eitherconductive barrier 16 or dielectric surface 17 on the other hybrid bondsurface according to the present invention. This feature can facilitatethe formation of an electrical connection across the bond interface forsome structures, for example where conductor 13 is an Al routing surfacebuilt in an Al BEOL, when making electrical connections betweenconductor 13 on opposing surfaces is more challenging than makingelectrical connections between conductive barriers 16 on top ofconductors 13 on opposing surfaces.

The amount of dishing shown in FIG. 11 can affect the thermal budget ofa subsequent direct hybrid bond using these surfaces. For example, lessdishing can result in a lower thermal budget required to complete thehybrid bond after initially directly bonding opposed dielectric surfacesat low or room temperature due to less conductor 13 expansion requiredto form a metallic bond between opposed conductive barrier 16 surfaces.

In a third embodiment according to the invention, a hybrid surfaceincludes a conductive through silicon via (TSV) structures 23 and 35 asshown in FIGS. 13-15. Each figure shows two different structures, with(23) and without (25) a conductive barrier material layer 26, forconvenience of illustration, formed in a manner similar to FIGS. 1-4above. The TSVs extend through substrate 40 to contact metal conductor 4in substrate 41. The conductive material of TSV 23 and 25 can becomprised of a metal like Cu or W or a non-metal like polysilicon. Theconductive material can be adjacent to an insulating material 24 asshown in FIG. 13 or, as shown in FIG. 14 including substrate 42, mayhave a barrier layer 27 interposed between the conductive material andinsulating material.

In another example, TSV 23 and 25 may have an insulating barrier 28interposed between the conductive material and a semiconductor substrate43 as shown in FIG. 15. The TSV may be recessed with increased dishingas described in the first and second embodiments and a conductivebarrier 26 formed within this increased dishing as described in thefirst and second embodiments to form a hybrid bond surface with dishingsuitable for direct hybrid bonding. These types of surfaces may bedirect hybrid bonded to each other resulting in, for example a so-calledback-to-back direct hybrid bond if the TSV surface is exposed throughthe back of a CMOS structure. It is also possible to use one of thesehybrid bond surfaces to form a direct hybrid bond to the hybrid bondsurface formed on the front of a CMOS structure, for example on top of aCu BEOL or Al BEOL, to form a so-called front-to-back direct hybridbond.

In the present invention BEOL via fill metal can be fully encapsulatedwith a conductive barrier. Further, the present invention allows hybridbond fabrication to utilize dielectrics and conductive barrier materialsfor the direct hybrid bonding. The process window for a direct hybridbond process leveraging materials and/or processes currently qualifiedin CMOS BEOL foundries can be improved. The present invention alsoallows for lowering the adoption barrier for manufacturers to qualifydirect hybrid bond technology, produces a direct hybrid bond surfaceusing a combination of insulating dielectric and conductive barriermaterials that are used in CMOS BEOLs, can provide a method andstructure for a direct hybrid bond surface that suppresses hillockformation, and can reduce thermal budgets in direct hybrid bonding.

Applications of the present invention include but are not limited tovertical integration of processed integrated circuits for 3-D SOC,micro-pad packaging, low-cost and high-performance replacement of flipchip bonding, wafer scale packaging, thermal management and uniquedevice structures such as metal base devices. Applications furtherinclude but are not limited to integrated circuits likebackside-illuminated image sensors, RF front ends, micro-electricalmechanical structures (MEMS) including but not limited topico-projectors and gyros, 3D stacked memory including but not limitedto hybrid memory cube, high bandwidth memory, and DIRAM, 2.5D includingbut not limited to FPGA tiling on interposers and the products thesecircuits are used in including but not limited to cell phones and othermobile devices, laptops, and servers.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

The invention claimed is:
 1. A structure, comprising: a direct hybridbond surface of an element, said direct hybrid bond surface comprising:a dielectric layer, conductive contact structures, and a firstconductive barrier material layer formed directly on an upper surface ofeach of said conductive contact structures, wherein an upper surface ofsaid first conductive barrier material layer is recessed below an uppersurface of said dielectric layer, said upper surface of said firstconductive barrier material layer comprises a contact surface configuredto contact another element.
 2. The structure according to claim 1,wherein a top surface of said conductive contact structures is belowsaid upper surface of said dielectric layer by about 5-40 nm.
 3. Thestructure according to claim 1, comprising a second layer of conductivebarrier material on a bottom and sides of said conductive contactstructures.
 4. The structure according to claim 1, wherein said firstand second layers of conductive barrier material completely surroundsaid conductive contact structures.
 5. A bonded structure, comprising:first and second direct hybrid bond surfaces on first and secondrespective elements, each of the first and second direct hybrid bondsurfaces comprising: a dielectric layer, conductive contact structures,and a first conductive barrier material layer formed directly on anupper surface of each of said conductive contact structures, said firstconductive barrier material layer comprising a contact surface, whereinsaid first conductive barrier material layers are disposed between saidupper surfaces of said conductive contact structures of each of saidfirst and second hybrid bond surfaces, and said dielectric layers insaid first and second direct hybrid bond surfaces are in direct contactwith and directly bonded to each other and said first conductive barriermaterial layers in said first and second direct hybrid bond surfaces arein direct contact with each other.
 6. The structure according to claim5, comprising a second conductive barrier material layer disposed on abottom and sides of said conductive contact structures.
 7. The structureaccording to claim 6, wherein said first and second conductive barriermaterial layers completely surround said conductive contact structures.8. The structure according to claim 5, wherein said dielectric layer isdisposed around said first conductive barrier material layers.
 9. Thestructure according to claim 8, wherein a second conductive barriermaterial layer on said sides of said conductive contact structures isdisposed along at least a portion of a periphery of said conductivestructures extending nonparallel to a bonded surface of said dielectriclayers.
 10. The structure according to claim 5, wherein said firstconductive barrier material layers comprise upper surfaces, saidconductive barrier material layers in said first and second directhybrid bond surfaces are in direct contact with each other at said uppersurfaces.
 11. The structure according to claim 10, wherein each of saidfirst conductive barrier material layers comprises a lower surfaceopposite said upper surface of said first conductive barrier materiallayers, the lower surface is in direct contact with said conductivecontact structure.
 12. The structure according to claim 10, wherein saidupper surfaces of said first conductive barrier material layers areapproximately coplanar with said first and second direct hybrid bondsurfaces.
 13. The structure according to claim 1, wherein said uppersurface of said first conductive barrier material layer is recessedabout one to ten nm below the upper surface of said dielectric layer.14. The structure according to claim 1, wherein said upper surface ofsaid first conductive barrier material layer is recessed such that acavity is formed on said upper surface of said first conductive barriermaterial layer.